How to Verify the Accuracy of Your IR Thermometer Using an Ice Bath- IR Thermometer Calibration Procedure

with 22 Comments
IR thermometer calibration using ICE BATH

Is your IR thermometer accurate? How do you know that your Infrared thermometer displays a correct reading after long use and exposure to different environmental conditions?

Safety in our daily operations is one of the main priorities during monitoring. Safety in terms of machine functionality and safety for the person involved. In terms of temperature monitoring, IR thermometer is one of the best-invented instruments that you can use without going near to a super hot object with a fast and reliable result.

As we can see, monitoring instruments like the IR thermometer gun needs to be accurate in order to be reliable and to properly detect the temperature of a body that is being monitored. Any inaccuracy will result in a problem – “your health and safety depend on it therefore we need to have a proper verification procedure that is fast and simple to perform”.

This is where the importance of IR thermometer calibration comes in. And during calibration, we need to perform verification in order to detect any out of specifications.

Please take note that this procedure is not applicable for Non-Contact thermometer used on skin or for medical purposes. The IR thermometer that I am referring to is the IR Thermometer used in different industries for monitoring processess and safety.

In this post, I will share with you the following:

  1. What is an Ice bath?
  2. How to create a simple ice bath?
  3. What is an IR thermometer?
  4. How to calibrate the Infrared thermometer using an ice bath?
  5. How to perform verification to determine the accuracy of IR thermometer

What is an Infrared (IR) Thermometer

An Infrared thermometer, also known as IR thermometer is a thermometer that is a non-contact type, which means it can measure a body’s temperature without making contact. It utilizes the radiated energy emitted by the body to detect and display as temperature.

What is the purpose of an IR thermometer?

We are using an IR thermometer, specifically the IR thermometer gun to measure temperatures that:

  1. Hard to reach areas
  2. Dangerous equipment like  moving machinery
  3. Needs social distancing – for body temperature monitoring at a distance,  just point and measure
  4. That needs faster response and results for immediate monitoring

Infrared thermometer works using the principle of the emissivity.  The emissivity of the surface of a material is its effectiveness in emitting energy as thermal radiation which is compared to a blackbody at the same temperature. A perfect blackbody has an emissivity of 1.

Read more about emissivity here >> emissivity

The default emissivity settings of most IR thermometer is 0.95.

When you are using an IR thermometer, the best results will be achieved if the emissivity of the object matches that of the IR thermometer settings. Some Infrared thermometers have an emissivity value that can be adjusted easily. Check this emissivity table for more emissivity value here >> emissivity table

In this post, I will present a calibration and verification in a zero point range using an ice bath with an emissivity of 0.97.

What is an ICE bath? 

An ice bath is one of the oldest and simplest zero-point temperature source reference standards used in temperature calibration. It is a temperature comparator where we compare the reading of the UUC to an actual 0 ℃ fixed-point range.  As the name implies, it is a simple combination of ice (shave or cube) and water that generates approximately 0.01 ℃ (0°C /32°F) temperature.

A properly prepared ice bath will give an accuracy or uncertainty of 0.002 ℃ (as per ASTM E563-11). This means that the lowest error (uncertainty) you can get when measuring an ice bath is 0.002 ℃ which is already negligible when using a simple thermometer with a resolution of 0.1℃.

Therefore, if you are measuring an instrument using an ice bath, you should read zero (0) (32°F) exactly.

For immediate calibration and verification, the ice bath is the best and easiest way to use as a reference standard. You can even prepare it even in your office for a quick verification setup.

Other important uses of an ICE Bath:

calibrating a digital thermometer with a thermocouple probe in an Ice Bath
calibrating a digital thermometer with a thermocouple probe immersed in an Ice Bath
  1. For calibration of thermometers with thermocouple probes or RTD probes
  2. Calibration and verification of food thermometers
  3. Calibration of glass thermometers
  4. Used for cold-junction compensation for a thermocouple wire.

To know more about thermocouple and thermometer calibration, visit my other post here >> Temperature calibration

How to Make A Simple ICE BATH

Simple Steps On How To Create an Ice Bath.

Prepare enough water and ice cubes from purified (preferably distilled water) water. We are only aiming a result of approximately 0.0 ℃, so for this verification, it is not a problem to use regular purified water.

Step 1. Prepare the ice. If it is in big blocks, crush it to smaller sizes
Step 2. Prepare a container. A dewar flask is advisable but not required.
Step 3. Look for an ice shaver. Load the ice cubes to the ice shaver
Step 4. Shave enough amount where you can fill the container (dewar flask) at least ¾ or 75 percent.

This image has an empty alt attribute; its file name is image-222x300.png
Shaved ice using a simple ice shaver

. .
Step 5. Wash the shaved ice with purified water to remove any contaminants and impurities.
Step 6. After washing, drain the water in the ice properly. 
Step 7. Pour again the purified water until about  90% of the ice is soaked. See to it that the shaved ice will NOT float.
Step 8 Occasionally stir the mixture to avoid any lumps or spaces to form. Drain any excess water. 
Step 9  Wait for around 2 minutes, then your ICE BATH is ready.

Ice Bath preparation
Ice Bath preparation

How to Perform Calibration of IR Thermometer Using the Ice Bath

This is a simple calibration procedure designed to calibrate your IR thermometer at the Zero Deg C range only. A comparison from a known Zero value-the ice bath. If you need more accuracy at a higher range, it is advisable to send your IR thermometer to a qualified calibration lab.

One purpose of this procedure is to use it for Intermediate Check activity, part of quality control procedure to ensure accuracy and proper functioning of your instrument.

Now, below are the steps to perform IR thermometer calibration using the Ice Bath:

1. Check the emissivity settings of the Infrared Thermometer gun, it should be within 0.95 to 0.97. A shave ice has an emissivity of 0.97.

IR thermometer emissivity value
emissivity value setting

2. Position the IR thermometer to the ICE bath where the distance of the tip and the ice is about 1 to 2 inches. This will ensure that the sensor’s field of view is inside the container.

3. Press the trigger button for 5 seconds to start measuring

4. Get the reading then record

IR thermometer calibration using an Ice Bath.
IR thermometer calibration using an Ice Bath through direct comparison

5. Perform the procedure 3 times.

6. Get the average of the results then calculate the error.

Measurement Data Sheet: records of calibration results

How to calculate Error:

Error = UUC(Average) – STD

         = 0.5 – 0.0

 Error = 0.5 ℃

Note: This is considered as partial calibration (single point) used for verification at the lower range only. If you are using your IR thermometer for higher ranges (above 100 deg C) with strict tolerance, you need to send it to a qualified calibration lab.

How to Perform Verification to Determine the Accuracy of IR Thermometer

  1. If you already have a set tolerance, then skip steps 2 to 5
  2. Get the manufacturer’s manual of the IR thermometer.
  3. Refer to the specifications and get to the  ‘Accuracy’ part. See the sample accuracy specs below.

  4. As per the above example, the accuracy at 0 ℃ = +/- 2.0. Now, this is also your tolerance limit
  5. The tolerance interval is 0+/-2 = -2 to 2
  6. Now, get the error from the result of the calibration above. Your reading should stay within these limits in order to be acceptable. See the below presentation to explain more.

  7. If it is outside this range, you need to perform an adjustment or send the thermometer to a qualified calibration lab for adjustment and full calibration.

    I have seen a good example of ‘How to adjust an IR thermometer’ (this may apply to your IR thermometer). See the below video…

8. End.

To know more about error and tolerance, visit this link>> Differences Between Accuracy, Error, Tolerance, and Uncertainty in a Calibration Results

Note: I get commissions for purchases made through links in this post.


The ice bath is the simplest and yet one of the most used reference standards for temperature calibration when properly prepared, it can provide an accuracy of 0.002 ℃. Enough to be used for an IR thermometer gun and other temperature instruments at a reference of ZERO Degree Celsius.

In this post, I have shared:

  1. What is an ICE bath?
  2. How to make a simple ice bath?
  3. What is an IR thermometer
  4. How to Calibrate the IR thermometer using an ice bath?
  5. How to perform verification to determine if the display of your IR thermometer is accurate.

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22 Responses

  1. Ajis
    | Reply

    Can we use the industrial IR Thermometer for medical (to measure human body)?

    • Hi Ajis,

      Industrial IR thermometers are meant for industrial use and it is not advisable to use in the human body. IR thermometer for medical or for human use has higher accuracy compared to industrial IR thermometers. It has tolerances that are far more strict than that of industrial use.

      I hope this helps,

  2. Eric Marcelo
    | Reply

    Very timely. ‘Will share this to disseminate the awareness that these things need to be checked before using. Pity the person who is told that he has a fever when, in fact, he doesn’t. Plus the possibility that a person with a fever is let through and contaminates the whole bank!

    I would add that emissivity is also dependent on the person’s skin color. Dark-colored skin will give a higher temperature reading than light-colored skin. I don’t know how much the difference is but the user must take that into account.

    • Hi Sir Eric,
      Very True. This is just a simple check but I hope that this will give awareness regarding the importance of using a calibrated instruments specially the IR thermometer at this time of crisis, in which it is used now as a basis to acccept or reject an individual.

      With regards to emissivity, Yes, we need to determine the actual emissivity and calculate any corrections during the actual calibration.

      Thanks for the additional inputs.

      Best regards,

      • Charlie
        | Reply

        Sir can i use your site for reference as part of our company’s internal calibration and maintenace procedures related documentation?

        • Hi Charlie,
          Yes, please feel free to use my site as per your needs. I appreciate it.

          Thanks and regards,

  3. Hallo,
    Thank you for that. Just to add some experiences how to expand the “calibration”: you can use a cup with boiled water. Surface temperature should be near 100°C – but on ocean level (pressure there). So the user should calculate what is the boiling temperature at the level over ground at the point where the “calibration” should start. But the user will get an second measurement (calibration) point.
    But: we speake about a tolerance of +/- 2K or 2% of reading – what ever is greater – for an industrial measurement device. Medical devices have got a very small measurement range – very close to 37°C.
    For me would be the most important point what Eric wrote: the IR thermometer measures the surface temperature – nothing more, nothing less. Even from skin. Only a specialist can know why the skin temperature for this “checked” guy in this situation is high or low.
    Take care!
    VBR – Andy

    • Hi Andy,

      That is great! I did not try this one yet but as long as you have performed the validation condition that you just mention, it is a good way to expand your verification points using water which is also readily available. Thanks for sharing.

      I appreciate your comments.

      Best regards,

  4. Edwin C. Aromin
    | Reply

    I am interested in your electrical equipment calibration. Could you give me a quotation for the training? Thank you

    Edwin C. Aromin
    Tel no. 09172708069

    • Sir Edwin,

      Thank you for your interest. unfortunately, I am not yet providing training but I will be willing to offer in the future.
      I will let you know.

      Thanks for visiting my site.
      Best Regards,

  5. You are very professional in your field and I just joined this field. So can you help me. I’ll be thankful to you.
    Best regards,
    Ivs Canada.

    • Welcome to the field of Metrology. Thank you for visiting my site.
      Can you tell me what help do you need?

      Best regards,

  6. Nice! Great content thank you for sharing with us and I have learned from this article.

    • Hi Valmik,
      you are welcome. I am glad you liked it.

      Best Regards,

  7. hemanth
    | Reply

    hi sir, how to calculate distance to spot ratio in IR thermometer

    • hi Hemanth,
      There is a label in the unit with a distance to spot ratio, for example, a ratio of 1:4, the smallest number is the radius or size of the spot you want to check while the larger number is the distance. For a spot of 1 inch, the distance would be 4 inches.
      I hope this helps,

  8. Shareen
    | Reply

    Hi Sir,

    I would like to ask for example if my oven reading after calibration is below:
    Nominal value of the standard: 100C
    Oven’s reading after average : 100.4C
    Error: 100.4C – 100C= 0.4C
    Accuracy of the oven from 100℃ = +/- 0.5

    As per the above example, the accuracy at from 100℃= +/- 0.5.
    That mean, my tolerance limit is +/-0.5 = -0.5 to 0.5

    Is it correct?

    What should I do if the error is exceed the tolerance limit?

    • Hi Shareen,
      Yes, it is correct. Great!

      If the tolerance limit is exceeded, you need to perform an adjustment if possible to adjust, if not, then you need to use the correction factor. Check out my post here about the correction factor.

      Best regards,

  9. Hi, Very informative article. It is necessary to calibrate a thermometer to assure accurate readings, as the accuracy of a thermometer can drift over time. Thank You.

    • You are welcome, Thanks for visiting my site.
      Best regards,

  10. Francine
    | Reply

    I am a director of a Food Pantry and am responsible for checking the temperatures of items that have been in refrigeratorsand freezers that are being transported and I need to keep them frozen and/or cool enough to hand out to my clients.I purchased an infrared thermometer 5months ago. Can you instruct me on how to calibrate my thermometer to get the correct readings?
    I am not an engineer of any kind and was recently informed that I need to calibrate the thermometer…So please help

    • Hi Francine,
      Good day!
      First of all, thanks for visiting my site.

      I can help you calibrate your infrared (IR) thermometer with the proper tools.
      But first, I want to inform you that if the calibration is a requirement from a regulatory body, it should be performed by a qualified person, or to be sure, the thermometer should be sent to a qualified calibration laboratory. You will be provided with a calibration certificate after they calibrate your infrared as an evidence that it is calibrated.

      But if you only need to calibrate just to verify if the reading of your thermometer is accurate at a certain temperature, then it is ok and I can help you with that. Actually, I already presented it in the blog post that you have just visited. You can calibrate the thermometer at point Zero only. But this is ok since you are using your IR thermometer for cold storage.

      Just to summarize,
      1. You need an ice bath as your reference standard. An ice bath has a reference temperature of “0” zero degC.
      2. Once you have prepared the ice bath, you only need to focus or point the thermometer as seen in the photo.
      3. The reading of the thermometer should be zero as well or should be within the tolerance specified by the manufacturer in order to pass the verification. You can see the tolerance or accuracy of the IR thermometer on its manual.
      4. If not, you need to adjust or compensate the error.

      Remember that this process should be recorded or documented.

      I hope this helps, any other concerns just let me know.

      Best regards,

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